In recent years, public attention has been directed to subsurface soil/groundwater contamination by toxic wastes. Increased governmental and private resources have been devoted to both assessing the extent/concentration of the contaminants and also remediation.
The most commonly used technique for detecting subsurface contaminants is soil sampling. A bore hole is drilled to a desired depth, with a sample of the soil being physically collected. The sample is cataloged and sent to a laboratory to determine the type and concentrations of contaminants contained in the soil typically using solvent extraction techniques. This approach, while providing the accuracy and precision of laboratory analysis, is both slow and costly. Separate bore holes are usually drilled for each sample collected, and the transportation of the sample to the laboratory followed by analysis require days to weeks before the results are available.
Cone penetrometer technology has been developed as a solution to some of the problems associated with physical collection/laboratory analysis. Typically, a cone penetrometer is advanced or pushed through the soil by lengths of drilling rod or pipe that connect the probe to a hydraulic pushing device, typically located in a truck. The penetrometer can be configured to collect multiple samples as it is advanced through the soil or, in some situations, tests the soil samples in situ. According to one technology, the end of the penetrometer probe is opened, and then the probe is advanced slightly to collect a small sample of soil in a chamber within the probe. Gases are collected from the soil as it is moderately heated, and the gases carried through collection tubes to the surface. There, gas chromotomography can be performed to identify contaminants in the soil.
Existing in situ cone penetrometer technology finds only limited practical use due to its poor accuracy/precision. The efficiency with which the soil contaminants may be identified is relatively poor compared to laboratory soil analysis. For example, the effective sample size of the previously-mentioned probe is limited by the size of its chamber, which in turn is only some fraction of the probe""s overall width. Small sample sizes lead to low detection limits. Moreover, the existing technology generally provides a high level of inter-sample contamination. That is, the contaminants collected from earlier samples tend to accumulate in the probe, distorting the results of later sampling events.
The present invention is directed both to an improved in situ penetrometer probe and to a heated, flexible transfer line. In the preferred embodiment, they are implemented together in a penetrometer system in which the transfer line is used to connect the probe to the surface.
In general, the inventive probe comprises a heater that controls a temperature of a geologic medium surrounding the probe. At least one carrier gas port and vapor collection port are located on an side wall of the probe. The carrier gas port provides a carrier gas into the geologic medium, and the collection port captures vapors from the geologic medium for analysis.
The heating of the surrounding soil enables both the debinding of chemicals otherwise locked in the soil and the collection without the need to draw the soil into the probe as in some prior art designs. The location of the ports on the side wall of the probe offers a number of further advantages over the prior art configurations. First, the construction need not be overly complex. Carrier gas and collection lines can be terminated in the side wall without requiring moving parts. More importantly, however, is the fact that soil is not drawn into the probe. Thus, there are no contaminants trapped in the probe to undermine the accuracy of subsequent samples. Soil from earlier samples is stripped from the probe""s exterior as it is advanced for the next sampling. Thus, the inventive probe does not suffer from measurement accuracy or precision problems, when vapor samples are gathered at different depths.
In embodiments, at least one, but preferably two or more vapor collection ports are spaced around a circumference of the probe. Corresponding carrier gas ports are also circumferentially located around the probe. Alternatively, in other embodiments, multiple collection and carrier gas ports can be spaced axially along the probe.
In the preferred embodiment, the probe comprises a temperature transducer to detect the temperature of the geologic medium surrounding the probe. The heater is capable of raising the temperature of this medium to greater than 200xc2x0 C., and preferably to approximately 400xc2x0 C. or greater. These temperatures are substantially higher than those obtained in many prior art devices, which worked in the approximately 100xc2x0 C. temperature range. This shortcoming was one reason why the prior art failed to achieve accurate results. Research associated with the present invention has shown that the higher temperatures are required to debind many types of contaminants, especially semi-volatile organic compounds, from the soil.
In still other embodiments, the carrier gas, which is injected into the surrounding soil, may be heated. In this way the soil can be directly heated with hot gas thereby reducing or eliminating the need for the heater in the probe.
In general, the invention also relates to a method for thermally extracting subsurface chemicals from soil with a high water content. This method comprises first advancing a probe through the soil to a desired depth. The soil surrounding the probe is then heated to at least 100xc2x0 C., preferably 120xc2x0 C., while a carrier or similar gas is exhausted into the soil. This has the effect of pushing water vapor away from the probe""s collection port. After this is completed, the soil is heated to substantially higher than 100xc2x0 C., and vapor is collected from the soil. Since the moisture content of the surrounding soil has been substantially reduced, more contaminates are found in the collected vapor since high moisture tends to keep the contaminants in the soil.
In the preferred embodiment, before future sampling, any contaminants remaining in the collection line are preferably backflushed back out of the line.
In general, according to another aspect, the invention also features the heated transfer line system. In the system, at least one flexible collection line conveys a collected fluid, i.e., vapor sample. At least one flexible carrier gas line conveys a carrier gas to facilitate the collection of the sample. The collection line is also heated.
The flexibility of the line is required by the penetrometer system because the line must pass through the pipe sections when they are stacked, i.e., not connected. Specifically, the line should have a bending radius of approximately 10 inches or less. In the preferred embodiment, the bending radius is 4 inches or less.
The flexibility of the line also enables its use in other applications and thus the line is not limited to penetrometer systems. For example, in smoke-stack emissions or airport bomb detection, a flexible transfer line is useful to carry a vapor sample from some remote location to a collector/analyzer.
When implemented in a penetrometer system, the line must be relatively long, greater than 50 feet and as long as 300 feet. These lengths are required because the line must pass through the pipe section in the soil but also the disconnected sections stacked in the truck.
A number of different options may be used to heat the collection line. Heating filaments or other heating device may be laid with the line. In the preferred embodiment, however, the collection line is electrically conductive so that an electrical power source can generate a current through it. Therefore, the collection line""s internal resistance heats the line. In either case, the heating capability should be strong enough to raise the line""s temperature to at least 280xc2x0 C. to keep contaminants, particularly semi-volatile organic compounds, vaporized in the line and later remove any condensed water during backflushing. In the preferred embodiment, the line may be heated to 200-400xc2x0 C. These temperatures are needed to debind many chemicals from the line""s walls if adsorbed to ensure that subsequent samples are not tainted.
The high temperatures at which the collection line may be maintained distinguish the invention from penetrometer systems in the prior art. While prior art probes had capabilities to heat the soil, any semi-volatile organic compounds that were vaporized could not be carried to the surface. They condensed in the cooler transfer line. In contrast, the present line can be uniformly heated so that the compounds remain vaporized, allowing the carrier gas to transport them to the surface.
In the preferred embodiment, the collection line is surrounded by at least one thermally insulating layer. At least one electrically insulating layer is also used. A slippery layer promotes flexibility allowing layers to slip with respect to each other. The insulating layers are needed so that the collection line""s temperature may be uniformly maintained across it extended 100 foot or more length. A somewhat related requirement is the fact that the temperatures and electric fields generated around the line must not endanger the personnel operating the line even in wet environments. Thus, various layers must also keep the line""s surface temperatures low enough to avoid burns and seal the line to prevent shock.
The above and other features of the invention including various novel details of construction and combinations of parts, and other advantages, will now be more particularly described with reference to the accompanying drawings and pointed out in the claims. It will be understood that the particular method and device embodying the invention are shown by way of illustration and not as a limitation of the invention. The principles and features of this invention may be employed in various and numerous embodiments without departing from the scope of the invention.